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#include<iostream>
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#include<string>
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class Building1
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{
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  //告诉编译器 goodGay全局函数 是 Building1类的好朋友，可以访问类中的私有内容
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  friend void goodGay(Building1 * Building1);
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public:
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  Building1()
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  {
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    this->m_SittingRoom = "客厅";
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    this->m_BedRoom = "卧室";
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  }
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public:
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  std::string m_SittingRoom; //客厅
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private:
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  std::string m_BedRoom; //卧室
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};
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void goodGay(Building1 * building1)
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{
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  std::cout << "好基友正在访问： " << building1->m_SittingRoom << std::endl;
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  std::cout << "好基友正在访问： " << building1->m_BedRoom << std::endl;
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}
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void test1()
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{
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  Building1 b;
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  goodGay(&b);
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}
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int main() {
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  test1();
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  return 0;
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}

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#include<iostream>
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#include<string>
3

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class Building2;
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class goodGay2
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{
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public:
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  goodGay2();
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  void visit();
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private:
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  Building2* building;
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};
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class Building2
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{
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  //告诉编译器 goodGay2类是Building2类的好朋友，可以访问到Building2类中私有内容
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  friend class goodGay2;
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public:
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  Building2();
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public:
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  std::string m_SittingRoom; //客厅
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private:
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  std::string m_BedRoom;//卧室
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};
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Building2::Building2()
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{
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  this->m_SittingRoom = "客厅";
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  this->m_BedRoom = "卧室";
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}
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goodGay2::goodGay2()
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{
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  building = new Building2;
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}
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void goodGay2::visit()
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{
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  std::cout << "好基友正在访问" << building->m_SittingRoom << std::endl;
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  std::cout << "好基友正在访问" << building->m_BedRoom << std::endl;
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}
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void test2()
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{
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  goodGay2 gg;
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  gg.visit();
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}
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int main() {
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  test2();
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  return 0;
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}

1
#include<iostream>
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#include<string>
3

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class Building3;
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class goodGay3
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{
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public:
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  goodGay3();
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  void visit(); //只让visit函数作为Building3的好朋友，可以发访问Building3中私有内容
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  void visit2();
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private:
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  Building3* building;
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};
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class Building3
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{
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  //告诉编译器  goodGay3类中的visit成员函数 是Building3好朋友，可以访问私有内容
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  friend void goodGay3::visit();
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public:
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  Building3();
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public:
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  std::string m_SittingRoom; //客厅
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private:
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  std::string m_BedRoom;//卧室
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};
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Building3::Building3()
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{
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  this->m_SittingRoom = "客厅";
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  this->m_BedRoom = "卧室";
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}
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goodGay3::goodGay3()
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{
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  building = new Building3;
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}
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void goodGay3::visit()
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{
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  std::cout << "好基友正在访问" << building->m_SittingRoom << std::endl;
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  std::cout << "好基友正在访问" << building->m_BedRoom << std::endl;
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}
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void goodGay3::visit2()
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{
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  std::cout << "好基友正在访问" << building->m_SittingRoom << std::endl;
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  //std::cout << "好基友正在访问" << building->m_BedRoom << std::endl;
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}
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void test3()
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{
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  goodGay3  gg;
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  gg.visit();
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}
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int main() {
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  test3();
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  return 0;
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}